"Those are initiatives which other people have suggested to us and we've simply chronicled the submissions."

But Nationals Senate leader Barnaby Joyce has rejected suggestions the draft discussion paper was just a pre-election thought bubble.

"This has been worked on for nearly two years, travelling the countryside, examining sites over the past couple of years," Senator Joyce told reporters in Canberra.

"This is certainly not a thought bubble. This is a key policy.

"It goes to show the Australian people that whilst we have been in Opposition we can be diligently doing our homework and preparing ourselves for that opportunity if it comes, the honour of government."

'Three leaks in three weeks'

The Coalition's plan for more dams was initially leaked to News Limited newspapers, prompting ridicule from Labor.

"This is a story about water, dams and leaks," Labor frontbencher Craig Emerson told reporters in Canberra this morning.

"Mr Abbott has had three leaks in three weeks. This is a strange way to release policy."

Only the Opposition could come up with a dams policy where they have dams that will be always full, always empty and always flowing.

Environment Minister Tony Burke

In Question Time, Environment Minister Tony Burke took delight in pointing out the "breathtaking logic" in the Coalition's dams plan.

"What they proposed... is that you can use your dams in this magical way that they will provide against drought, provide against flood and provide renewable energy," he said.

"If you're managing a dam to avoid drought, your dam has to be constantly full; if you're managing your dam to avoid floods, you need to keep your dam empty; and if you're managing your dam to be able to provide hydroelectricity, you need to keep your dam flowing.

"Only the Opposition could come up with a dams policy where they have dams that will be always full, always empty and always flowing."

Cost analysis

Dr Emerson says the Coalition now needs to explain how it is going to pay for the multi-billion-dollar dams plan.

"The Australian people expect the release of fully costed policies so that they know about the policies of both parties, and... where the money is coming from."

Mr Abbott says new dams would only be built after a thorough cost-benefit analysis but argues many projects would not need government funding.

"The proponents would fund them because the spin-offs - in terms of agricultural development, in terms of hydroelectric power, in terms of flood mitigation - are just really too good to ignore," he told Macquarie Radio.

The Greens have described the Coalition's discussion paper as "poorly thought through and environmentally reckless".

"While the Greens are releasing considered, costed policies, the Coalition are leaking crazy thought bubbles with $30 billion price tags that will devastate the environment," Greens senator Sarah Hanson-Young said in a statement.

"This is a pie-in-the-sky plan based on 19th-century thinking and the Coalition know they have no way to fund it."

She says the Greens support flood mitigation but says dams can put fisheries at risk and reduce water quality.